Climate-neutral energy supply is leading to a shutdown of fossil-fuelled power plants, higher electricity demand and higher transmissions and causes an increasing demand for grid inertia. In future, renewable energy sources with grid-forming capabilities will need to provide grid inertia in order to cover demand in a climate-neutral manner. The replacement of fossil-fuelled power plants with renewable energy sources, a change is not only observed in the technology itself, but also in the voltage level at which they are connected. In addition to larger power plant systems operating at extra-high and high voltage levels, renewable energy sources are distributed across medium and low voltage levels. Therefore, the paper investigates the equivalence of inertia power and inertia energy when supplied from different voltage levels.
In order to achieve this objective, a cross-voltage-level SimBench grid has been configured in PowerFactory, encompassing high, medium and low voltage levels, with a transfer station to the extra-high voltage level. In the reference grid, existing battery storage systems are dynamised using grid-forming models of virtual synchronous machines. A comparison between inertia provision of a single grid-forming battery storage system connected at the extra-high-voltage level and that of distributed battery storage systems from the distribution Grid is drawn. In dynamic RMS simulations, defined active power disturbances are applied and the frequency gradient, as well as the inertia power and energy, are evaluated. The investigation of this influence is conducted by considering various steady-state operating conditions and fault directions.